So apparently this seems like it can be locked out. I was turning in the keystone and spawned the giant. Other players right next to me (90s) killed it before I could even notice it spawned. No quest from the rock, though I do get the follow-up from the Dwarf at Refuge Point to kill the giant you first started the quest chain from.
Edit, ok my mistake. Once I abandoned the quest, I could then pick up the Myzrael's Tale starter from the stone at the circle.
As a note if this happens and you don't see the quest available from the stone at the circle, go back to Refuge Point, accept the quest to fight the Princess, cancel the quest, and then the original stone's turn-in should be available. Apparently the giant itself doesn't carry anything necessary.